In recent years, general purpose machine vision systems utilizing one or more television (TV) cameras and a high-speed digital processing system for image analysis have become available for a variety of image analysis applications. These vision systems typically include a variety of standard hardware and software features to perform various processing steps including image acquisition, feature enhancement, image segmentation, feature extraction and recognition of objects, and features and attributes thereof. The attributes of the objects or features which can be recognized or determined include location with a scene or buffer, area, centroid of the area, and orientation of the object or feature under scrutiny. These general purpose machine vision systems must be adapted and tailored to a specific application before they can serve any useful purpose in an industrial process setting. This is accomplished by proper selection and placement of vision hardware, which includes locating one or more cameras and providing proper lighting and camera filters (if needed), creating an applications software package or program to direct and control the operation of the vision system hardware, and interfacing the vision system to the electronic controllers operating or monitoring the process equipment.
Automated painting equipment, such as paint lines for automotive vehicle bodies and parts found around the world in the factories of automobile and truck manufacturers, presently utilize a significant number of photocell devices to identify objects and conditions so that the equipment may be properly operated in a safe and desired manner. For example, several photocell devices are typically used singly or in combination to automatically identify or verify the type of object approaching a paint spray station or booth within an automated paint line. Photocells are also often used to detect the intrusion of a human being into various zones of the paint line. They are also used to detect the arrival of a vehicle body at a predetermined location within the paint spray station or booth, which thus initiates a "zone start" or similar signal, that causes the applicators to begin spraying paint. As a final example, they are mounted on and move with movable paint bell support fixtures or platforms to ensure that a proper distance or minimum clearance will maintained between the paint bells on the fixture and the object or vehicle body being painted. In electrostatic paint spraying equipment, such nozzles are normally referred to as bells, to distinguish them from the conventional paint spray nozzles which work without the benefit of electrostatic forces upon the paint droplets emanating from the nozzles.
Up until the present invention, the photocell devices have been preferred for object identification, detection and sensing for automated painting equipment. They are preferred because they are non-contact devices which do not scratch the object (i.e., vehicle body or part) to be painted, are relatively reliable if properly maintained, and can be located so as to not interfere with the movement of the objects to be painted through the paint line. Yet, photocell devices have drawbacks. The photocell devices are easily fooled or disabled by mischievous workers or by environmental factors, such as dirt, dust, paint mist or splatter fogging over or otherwise obscuring the transparent protective covers of the photocells. Typically they must be cleaned often, perhaps as often as three times per eight hour work shift, in order to ensure that they will operate properly. Also, the photocell devices are rather expensive, particularly when the custom-designed placement, installation and hook-up costs (such as conduit runs and wiring) are included, with some estimates being as high as $1000.00 per photocell device. The photocell devices, if not critically aligned, often times will not properly identify an object. Moreover, the object to be identified must itself typically be precisely positioned upon its pallet or other holder that is normally carried along by a conveyor system, in order to be properly identified. The photocell devices may well incorrectly identify or not be able to identify an object if the object is slightly out of alignment upon its pallet or holder. Finally, the typical photocell device used on an automotive paint line has been estimated to add approximately one foot to the longitudinal dimension of such paint line, principally on account of the unobstructed, uncluttered space required for a clean or interference-free zone for the line of sight of the photocell beam. Thus, using photocell devices adds materially to the overall size and cost of the paint line.
In order to eliminate most (if not all) of the drawbacks associated with the use of photocells on paint lines and to permit the paint lines to be made physically smaller, I investigated the use of machine vision systems as a replacement or alternative for photocells. My work in this area led to my invention described below which offers numerous advantages over conventional photocell devices and associated methods for detecting and identifying objects and person entering or passing through automated painting equipment such as vehicle body paint lines. My work clearly indicates that machine vision systems with one or more television-type cameras can be used with painting equipment to: (1) replace photocells in many applications on paint lines; (2) increase equipment reliability; (3) reduce maintenance requirements; (4) improve the accuracy of the identification of objects and persons; (5) reduce set-up or change-over costs when objects to be painted having a different configuration (such as a new vehicle body style); (6) increase tolerance to misalignment of the objects to be painted on their work rests; and (7) save a considerable amount of space on the equipment such as a paint line as well, thus allowing more compact (and hence less expensive) paint lines to be constructed.